The enzymatic hydrolysis of sludge has been investigated for the last two decades and a number of enzymes from different organisms have been reported to play an important role in a range of waste water treatment applications. Enzymes act on specific substances present in municipal sludge and therefore can change the characteristics of the waste. The sludge becomes more amenable to further treatment and bio-conversion to value-added products is facilitated. Enzymatic treatment of mixed sludge prior to the anaerobic digestion shows degradation of the sludge and lead to methane production. Enzymatic treatment of wastewater sludge has a potential contribution to the reduction of sludge volume without biomass generation.
Enzymes break down polymeric substances like proteins, polysaccharides and lipids through multi step processes. Initially, enzymes adsorb to the solid substrate and cleave small polymers that are loosely bound to the surface. The solubilisation of the more compact sludge core occurs at a lower rate dependent on the diffusion of the enzyme to surface active sites and core particles. Previous studies have shown that a combination of a protease, lipase and endo-glycanases accelerated solubilisation of municipal sludge. However, the enzymes became entrapped in the sludge. The entrapment decreased the enzymes action on the sludge but not on chromogenic soluble substrates present.
In UK patent application 2 167 399 a method for hydrolytic enzymatic treatment of organic substances and biomasses is described. The method describes a step where a chelate-former in the form of di-ammonium and/or tri-ammonium salt of nitrile tri-acetic acid is added to the method in the presence of oxygen, i.e. an aerated or aerobic process. The hydrolytic enzymes degrade protein structures. The end products of an enzymatic treatment in an aerated environment are carbon dioxide and water.
In U.S. Pat. No. 5,783,081 a method of improving performance of an operating anaerobic solids digester comprising a step of adding at least one substantially pure culture of at least one methanogen is described. In an embodiment described therein a chelating agent, citric acid, is added to said digester. It is only the combination of microbes, e.g. bacteria, and chelating agents in an anaerobic environment that is described in the patent.
There still exists a need within the art to find new ways to increase the degradation of sludge in water purification in order to achieve more cost effective methods. The enzymes that are used today are very expensive and if alternative methods can be provided where less enzymes are used, industrial water purification plants will see the benefits of such cost-effective methods.